Performance enhancement by using string concat vs list joins.

Author: Jay Chan

pybars/_compiler.py

@@ -42,6 +42,7 @@
 except NameError:
     # Python 3 support
     str_class = str
+    basestring = str
 
 
 # Flag for testing
@@ -163,31 +164,43 @@ class PybarsError(Exception):
     pass
 
 
-class strlist(list):
+class strlist(object):
+    __slots__ = ['value']
+    def __init__(self, default=None):
+        self.value = u''
+        if default:
+            self.grow(default)
 
-    """A quasi-list to let the template code avoid special casing."""
+    def __str__(self):
+        return self.value
+
+    def __unicode__(self):
+        return self.value
 
-    def __str__(self):  # Python 3
-        return ''.join(self)
+    def append(self, other):
+        self.value += other
 
-    def __unicode__(self):  # Python 2
-        return u''.join(self)
+    def extend(self, other):
+        if type(other) is strlist:
+            self.value += other.value
+        else:
+            self.value += ''.join(other)
 
-    def grow(self, thing):
-        """Make the list longer, appending for unicode, extending otherwise."""
-        if type(thing) == str_class:
-            self.append(thing)
+    def __iter__(self):
+        return iter([self])
 
-        # This will only ever match in Python 2 since str_class is str in
-        # Python 3.
-        elif type(thing) == str:
-            self.append(unicode(thing))
+    def __add__(self, other):
+        self.value += other.value
+        return self
 
+    def grow(self, other):
+        if isinstance(other, basestring):
+            self.value += other
+        elif type(other) is strlist:
+            self.value += other.value
         else:
-            # Recursively expand to a flat list; may deserve a C accelerator at
-            # some point.
-            for element in thing:
-                self.grow(element)
+            for item in other:
+                self.grow(item)
 
 
 _map = {
@@ -212,14 +225,15 @@ def escape(something, _escape_re=_escape_re, substitute=substitute):
 
 
 def pick(context, name, default=None):
-    if isinstance(name, str) and hasattr(context, name):
+    if type(name) is str and hasattr(context, name):
         return getattr(context, name)
     if hasattr(context, 'get'):
         return context.get(name)
     try:
         return context[name]
     except (KeyError, TypeError):
-        return default
+        pass
+    return default
 
 
 sentinel = object()
@@ -270,34 +284,40 @@ def __unicode__(self):
         return unicode(self.context)
 
 
+ITERABLE_TYPES = (list, tuple)
+
 def resolve(context, *segments):
-    carryover_data = False
 
+    context_type = type(context)
     # This makes sure that bare "this" paths don't return a Scope object
-    if segments == ('',) and isinstance(context, Scope):
+    if segments == ('',) and context_type is Scope:
         return context.get('this')
 
+    carryover_data = False
     for segment in segments:
 
+        if context is None:
+            return None
+
         # Handle @../index syntax by popping the extra @ along the segment path
         if carryover_data:
+            segment = u'@' + segment
             carryover_data = False
-            segment = u'@%s' % segment
-        if len(segment) > 1 and segment[0:2] == '@@':
+
+        if segment[:2] == '@@':
             segment = segment[1:]
             carryover_data = True
 
-        if context is None:
-            return None
-        if segment in (None, ""):
+        if not segment:
             continue
-        if type(context) in (list, tuple):
-            offset = int(segment)
-            context = context[offset]
-        elif isinstance(context, Scope):
+
+        if context_type is Scope:
             context = context.get(segment)
+        elif context_type in ITERABLE_TYPES:
+            context = context[int(segment)]
         else:
             context = pick(context, segment)
+        context_type = type(context)
     return context
 
 
@@ -336,7 +356,7 @@ def prepare(value, should_escape):
 
 
 def ensure_scope(context, root):
-    return context if isinstance(context, Scope) else Scope(context, context, root)
+    return context if type(context) is Scope else Scope(context, context, root)
 
 
 def _each(this, options, context):
@@ -509,8 +529,8 @@ def start(self):
             ])
         else:
             self._result.grow(u"def %s(context, helpers, partials, root):\n" % function_name)
-        self._result.grow(u"    result = strlist()\n")
         self._result.grow(u"    context = ensure_scope(context, root)\n")
+        self._result.grow(u"    result = strlist()\n")
 
     def finish(self):
         lines, ns, function_name = self.stack.pop(-1)
@@ -521,7 +541,7 @@ def finish(self):
             self._result.grow(u"        result = %s(result)\n" % str_class.__name__)
         self._result.grow(u"    return result\n")
 
-        source = str_class(u"".join(lines))
+        source = str_class(lines)
 
         self._result = self.stack and self.stack[-1][0]
         self._locals = self.stack and self.stack[-1][1]
@@ -578,11 +598,12 @@ def add_block(self, symbol, arguments, nested, alt_nested):
             u"        value = helper(context, options%s\n" % call,
             u"    else:\n"
             u"        value = helpers['blockHelperMissing'](context, options, value)\n"
-            u"    result.grow(value or '')\n"
+            u"    if value:\n"
+            u"        result.grow(value)\n"
             ])
 
     def add_literal(self, value):
-        self._result.grow(u"    result.append(%s)\n" % repr(value))
+        self._result.grow(u"    result.value += %s\n" % (repr(value),))
 
     def _lookup_arg(self, arg):
         if not arg: